U.S. patent application, Ser. No. 09/774,852, filed Jan. 31, 2001, of Michael Kurt Gordon et al for xe2x80x9cFinisher With Sheet Placement Control.xe2x80x9d U.S. patent application Ser. No. 09/793,360, filed Jan. 31, 2001, of Jeffery Allen Ardery et al for xe2x80x9cFinisher With Frictional Sheet Mover.xe2x80x9d U.S. patent application of Daniel Mlejnek et al for xe2x80x9cFinisher With Single Roller For Frictionally Moving Each Sheet,xe2x80x9d Ser. No. 09/822,982, filed on even date herewith. U.S. patent application of Thomas C. Wade for xe2x80x9cOutput Tray Having An Increased Capacity For Stapled Sheets,xe2x80x9d Ser. No. 09/822,614, now abandoned. filed on even date herewith.
This invention relates to a sheet beam breaker for breaking a longitudinal beam if it is created in a sheet being fed from sheet paper exit rollers after the sheet exits from the exit rollers and falls by gravity onto a support surface and, more particularly, to a sheet beam breaker that breaks a longitudinal beam created in a sheet being fed from sheet path exit rollers in which each sheet exits from the exit rollers and falls by gravity onto a support surface and creates a lateral beam in the sheet in the direction of alignment after removing the longitudinal beam.
When sheets are fed from sheet path exit rollers for disposition in a stack on lower support surfaces to which each sheet falls by gravity, the sheet is not constrained when it falls onto the support surfaces. Accordingly, the sheet is free to take whatever form or shape is induced in the sheet by the sheet""s internal stresses.
It is well known that internal stresses are induced in a sheet during the fusing process in a laser printer. These internal stresses cause the sheet to curl. The shape of the curl that is of interest in this invention is curl that is parallel with the length of the sheet and is referred to as L curl. The L curl significantly increases the beam strength in a sheet in the longitudinal direction; therefore, the sheet can be referred to as having a longitudinal beam.
In a finishing device, it is desirable to have sheets with consistent shape and form during the alignment of sheets at a predetermined location for consistent sheet to sheet registration. It also is desirable to have increased beam strength in the alignment direction to decrease the possibility of buckling of the sheet between aligning device and the alignment reference barrier. The desired increase in beam strength can be obtained by inducing in the sheet a form that curls the sheet such that the curl is parallel with the width of the sheet and is referred to as a W curl. Sheets with the W curl can be referred to as having a lateral beam.
To achieve a small compact design for the finishing device, the sheet that has exited the exit rollers and falls is supported on two support surfaces. The first support surface supports the rear portion of the sheet and is the area where the alignment mechanism exerts the forces on the sheet to move the sheet to the predetermined alignment location.
The second surface supports the front portion of the sheet. This second support surface also serves as the output bin for sheets that have been finished in the finisher.
Between these two support surfaces, there is a portion which is lower than the two support surfaces for the sheet. This lower portion is for the trailing edge of the sheets to fall into after they are fed into the output bin so that the next sheet""s leading edge will be fed over the trailing edge of the sheets in the output bin. This configuration produces two support surfaces with a significant gap between them such that sheets may droop in the lower center portion. This droop would form the desired W curl that would increase the beam strength in the sheet in the alignment direction.
The initial few sheets falling onto the support surfaces usually droop in the middle due to the gravitational forces exceeding the internal stresses that try to form a longitudinal beam. Therefore, a lateral beam is formed which aids in consistent alignment of the sheets at a predetermined location.
However, as the stack of sheets increases in height, the possibility exists that a sheet will not droop due to the lower sheets supporting the upper sheet thereby not allowing the gravitational forces to overcome the internal stresses in the sheet. When this occurs, a longitudinal beam may form in the sheet. This sheet with the longitudinal beam will have a different form and lower beam strength in the direction of alignment than the sheets beneath it. This condition of having a different form in the upper sheet (longitudinal beam) to the form of the initial sheets (lateral beam) will result in poor registration of the upper sheet relative to the sheets beneath it.
This lack of consistency of sheets having consistent lateral beam forms has a significant effect on alignment of a plurality of sheets in a stack. Thus, for best alignment purposes, each sheet must have substantially the same form or shape, which is a lateral beam form, when it is disposed on its support surfaces prior to being moved therealong for alignment at a predetermined location. This is particularly important when the sheets are to be stapled to each other after being aligned at the predetermined location as shown and described in the aforesaid Mlejnek et al application.
The sheet beam breaker of the present invention is capable of breaking a longitudinal beam existing in each sheet of paper or similar material falling by gravity after the sheet leaves sheet path exit rollers and is contacted by the sheet beam breaker as both the sheet beam breaker and the sheet simultaneously fall by gravity. In addition to breaking a longitudinal beam existing in any sheet that it contacts, the sheet beam breaker of the present invention also creates a beam in a lateral direction in the same sheet through exerting a lateral downward force on the sheet to create a lateral beam therein after the longitudinal beam is broken by the lateral downward force. This increased beam strength in the lateral direction aids in alignment of each sheet when the sheet is moved laterally on the support surface for alignment at the predetermined position at which the sheets are stacked and then stapled, if desired. It also insures that the sheets have substantially the same desired form or shape.
The support surfaces have at least a portion lower than the remainder of the support surfaces to provide a gap at which the droop is produced in each sheet when it is supported by the support surfaces. In the preferred embodiment, the sheet is supported on front and rear support surfaces with a lower portion between the front and rear support surfaces. Alignment of each sheet occurs on the rear portion of the support surfaces.
The sheet beam breaker is preferably a wire bail. It also preferably extends for more than half of the width of each sheet and is disposed symmetrically relative to the desired location of each sheet as the sheet falls onto the support surface.
Because the sheet beam breaker is part of a pivotally mounted bail actuator, which must be pivotally moved by the sheet during its exiting from the sheet path exit rollers, the bail actuator must not weigh more than the sheet exiting the exit rollers can support. While it would be preferred for the wire bail to extend over the entire width of the sheet, this would increase the weight of the bail actuator, and the bail actuator could not be pivoted by the sheet due to the increased weight.
An object of this invention is to provide a sheet beam breaker for breaking a longitudinal beam created in a sheet falling by gravity after being fed by sheet path exit rollers and with which the sheet beam breaker contacts as both fall by gravity.
Another object of this invention is to provide a sheet beam breaker capable of controlling the direction of a beam in a sheet falling to a support surface by gravity after its exit from sheet path exit rollers.
Other objects of this invention will be readily perceived from the following description, claims, and drawings.